System and method of media content streaming with a multiplexed representation

ABSTRACT

In accordance with an embodiment, a method of operating a streaming media client includes electronically receiving, from a network, information regarding component access points of a first multiplexed representation of a streaming content. The first multiplexed representation of the streaming content includes a plurality of media components, and each component access point defines an independently coded access point for one of the plurality of media components. The method further includes selecting a first segment of the first multiplexed representation of the streaming content based on the information regarding the component access points, and requesting the selected first segment of the first multiplexed representation of the streaming content from the network.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional ApplicationNo. 61/494,806 filed on Jun. 8, 2011, entitled “System and Method ofHTTP Streaming with Multiplexed Representation,” which application isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to communication systems, andmore particularly to a system and method for media content streamingwith multiplexed representations.

BACKGROUND

As the capability of IP networks and network infrastructure hasincreased, and the quality of Internet-based video streaming technologyhas improved, the popularity of Internet streaming for videodistribution has increased tremendously. One common method ofimplementing streaming video is transmitting the video program from aHypertext Transfer Protocol (HTTP) server to a web-based HTTP client.Web-based streaming video is pervasive because of the simplicity ofaccess, in that a user simply clicks on a link to view video content.

Video streaming technology faces some difficulties, however. In somecases, when a user requests video content, there can be a considerabledelay before the content starts playing. In some cases, streaming videocontent is interrupted or stalled because of heavy network and/or poorlink conditions. In other cases, even if the network link initiallystarts out good, the viewing experience may be later degraded due tochanging network conditions.

SUMMARY OF THE INVENTION

In accordance with an embodiment, a method of operating a streamingmedia client includes electronically receiving, from a network,information regarding component access points of a first multiplexedrepresentation of a streaming content. The first multiplexedrepresentation of the streaming content includes a plurality of mediacomponents, and each component access point defines an independentlycoded access point for one of the plurality of media components. Themethod further includes selecting a first segment or subsegment of thefirst multiplexed representation based on the information regarding thecomponent access points, and requesting the selected first segment orsubsegment of the first multiplexed representation from the network.

In accordance with a further embodiment, a method of operating astreaming media server includes electronically transmitting to a clientinformation regarding component access points of a first multiplexedrepresentation of a streaming content. The first multiplexedrepresentation of the streaming content includes a plurality of mediacomponents, and each component access point defines an independentlycoded access unit for one of the plurality of media components. Themethod further includes receiving a request from the client for a firstsegment or subsegment of the first multiplexed representation of thestreaming content according to a selected component access point, andtransmitting the requested first segment or subsegment of the firstmultiplexed representation of the streaming content to the client.

In accordance with a further embodiment, a system for receivingstreaming media content includes a communications adapter and aprocessor. The communication adapter receives information regardingcomponent access points of a first multiplexed representation of astreaming content from a network, wherein the first multiplexedrepresentation of the streaming content includes a plurality of mediacomponents, and each component access point defines an independentlycoded access unit for one of the plurality of media components. Theprocessor selects a first segment or subsegment of the first multiplexedrepresentation of the streaming content based on the informationregarding the component access points, and requests the selected firstsegment or subsegment of the first multiplexed representation of thestreaming content.

In accordance with a further embodiment, a non-transitory computerreadable medium having an executable program stored thereon thatinstructs a microprocessor to perform the steps of receiving, from anetwork, information regarding component access points of a firstmultiplexed representation of a streaming content, selecting a firstsegment or subsegment of the first multiplexed representation of thestreaming content based on the information regarding the componentaccess points, and requesting the selected first segment or subsegmentof the first multiplexed representation of the streaming content fromthe network. The first multiplexed representation of the streamingcontent includes a plurality of media components, and each componentaccess point defines an independently coded access unit for one of theplurality of media components.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a media streaming system;

FIGS. 2a-c illustrate an embodiment data structures;

FIGS. 3a-b illustrate embodiment streaming methods;

FIGS. 4a-b illustrate further embodiment streaming methods;

FIGS. 5a-b illustrate other embodiment streaming methods;

FIG. 6 illustrates a computer system for implementing embodimentmethods; and

FIG. 7 illustrates a further computer system for implementing embodimentmethods.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the present inventionprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

The present invention will be described with respect to embodiments inspecific contexts, for example, a system and method for media contentstreaming. In particular, some embodiments relate to streaming of mediacontent based on the HTTP protocol.

FIG. 1 illustrates HTTP-based media content streaming system 100 thatimplements concepts and methods of the present invention. System 100 hasHTTP streaming server 102 that transmits streaming media to HTTPstreaming client 106 via IP network 104. It should be appreciated thatalternative embodiments can also be directed toward other streamingsystems besides HTTP streaming systems.

Embodiments of the present invention utilize systems and methods forHTTP streaming of multimedia streams of audio and/or video and/or othermedia types.

Streaming refers to the multimedia service where users simultaneouslyreceive and playback media contents. Conventional streaming solutionsuse the protocol set of RTP/UDP/IP for transport of media data,encapsulated as RTP packets, and use RTSP for session control and SDPfor session description.

HTTP adaptive streaming refers to the streaming service wherein the HTTPprotocol is used for transport of media data. In HTTP adaptivestreaming, the protocol set of HTTP/TCP/IP is used for transport ofmedia data, “encapsulated” as files or parts of files, HTTP is used forthe control of the streaming processes, and XML is typically used fordescription of the media. The description is typically referred to asmedia presentation description (MPD) or manifest.

Compared to RTSP/RTP based streaming, HTTP adaptive streaming isadvantageous in that it has the ability to use standard servers andstandard HTTP caches, or inexpensive servers in general, to delivercontent from a CDN or any other standard server farm. Furthermore, HTTPadaptive streaming ability to move control of “streaming session”entirely to the client, which basically only opens one or several TCPconnections to one or several standard HTTP servers or caches. HTTPadaptive streaming may also enable easy and effortless streamingservices by avoiding Network Address Translation (NAT) and firewalltraversal issues, and enables start of the streaming process aftertransmitting fewer protocol messages. While Forward Error Correction(FEC) may be needed in some RTSP/RTP based streaming systems, it may notbe required in HTTP adaptive streaming. Therefore, overhead caused byFEC may be reduced.

Thanks to these advantages, HTTP adaptive streaming has become popularrecently and has been adopted by many companies as a way to delivervideo through the Internet. Success stories of HTTP adaptive streaminginclude smooth streaming of Microsoft Silverlight, dynamic streaming ofAdobe Flash, quantum streaming of Move Networks, and live streaming ofApple. Standard development organizations, such as 3GPP, OIPF (the OpenIPTV Forum), and MPEG have been working towards international standardson HTTP adaptive streaming. 3GPP completed its Release 9 Adaptive HTTPStreaming (AHS) standard in March 2010 and the its Release 10 3GPPDynamic Adaptive Streaming over HTTP (3GP-DASH) standard in June 2011,and OIPF has completed its HTTP Adaptive Streaming (HAS) standard inAugust 2010. MPEG's Dynamic Adaptive Streaming over HTTP (DASH) standardwas completed in July 2011.

Both conventional RTSP/RTP-based streaming and HTTP adaptive streamingallow a streaming server to provide multiple versions of a mediacontent, which may differ in spatial resolution, bit rate, frame rate,and so on. Clients may choose an appropriate content version at thebeginning of the streaming process based on the connecting bandwidth,the client's capabilities as well as user preferences. By provisioningof multiple content versions, clients may also perform stream adaption.For example a client may start streaming at a first bit rate, but laterswitch to a different bitrate when the connecting network bandwidthchanges during a streaming session.

OIPF HAS and MPEG DASH specify support for two types of streamingcontents: one based on ISO base media file format (ISOBMFF, also widelyreferred to as MP4 file format); and one based on MPEG-2 TransportStream (TS). 3GPP AHS, on the other hand, only specifies support forISOBMFF based streaming contents.

Among the existing HTTP adaptive streaming approaches, including 3GPPAHS, OIPF HAS, and MPEG DASH, there lacks a mechanism for efficientsupport of multiplexed representations. A multiplexed representationrefers to a representation that contains more than one media component.A media component is an encoded version of one individual media typesuch as audio, video or timed text with specific attributes, e.g.bandwidth, language, or resolution. In particular, the cases wherein atleast two of the media components contained (also referred to asmultiplexed) in a representation were encoded in such a way that not allaccess units are independently coded were not supported by conventionalsystems.

FIG. 2a illustrates various ways of components being combined intovarious multiplexed representations. In one example two video sources,VIDEO 1 and VIDEO 2, and two audio sources AUDIO 1 and AUDIO 2, arecombined into four multiplexed representations. For example multiplexedrepresentation 1 combines VIDEO 1 and AUDIO 1. Remaining representations2-4 denote other combinations of the video and audio sources. In oneembodiment, VIDEO 1 may be associated with a 1 Mbps video stream, andVIDEO 2 may be associated with a 2 Mbps video stream. Likewise, AUDIO 1may be associated with an English language audio stream, and AUDIO 2 maybe associated with a Spanish language audio stream. FIG. 2b provides anexample of how these various streams may be multiplexed.

It should be appreciated that the embodiments shown in FIGS. 2a-b aresimple illustrative examples of many possible embodiment multiplexedrepresentations. In embodiments of the present invention, video andaudio streams may be included in any number of differentrepresentations. Furthermore, other types of streaming data may also beincluded along with video and/or audio streams.

For simplicity of description, described embodiments are directed towardMPEG-based systems described the in following standards documents, whichare incorporated by reference herein in their entirety: MPEG outputdocument W11930 (v2): Study Text of ISO/IEC 23001-6: Dynamic adaptivestreaming over HTTP (DASH) DIS; and on MPEG output document W11921: Textof ISO/IEC 14496-12:2008|15444-12:2008 (3rd edition)/Amendment 3: DASHsupport and RTP reception hint track processing. It is understood,however, that the inventive concepts can be applied to other situationsas well.

Embodiments of the invention may provide one or more of the following:an improved definition of Representation Access Point (RAP); a newlyintroduced definition of a Component Access Point (CAP); an improvedmechanism for identifying and signaling of media segments or subsegmentsstarting with a Representation Access point in a multiplexedrepresentation; an improved mechanism for signaling of representationaccess points and/or component access points in media segments of amultiplexed representation; and an improved mechanism for signaling ofthe presentation time of the first representation access point and/orcomponent access points in a sub-segment in a media segment of amultiplexed representation.

A Representation Access Point (RAP) is a position in a representationthat is identified as being a position for which it is possible to startplayback using only the information contained in data in therepresentation starting from that position onwards. In some embodiments,playback is preceded by initialising with an initialisation segment, ifany.

In an embodiment, each RAP is associated with two properties: I_(RAP)and T_(RAP). T_(RAP) is the earliest presentation time such that, foreach media component contained in the representation, all access unitswith presentation time greater than or equal to T_(RAP) can be correctlydecoded using data in the Representation starting at I_(RAP) and no databefore I_(RAP) (preceded by initialising with the InitialisationSegment, if any). I_(RAP) is the greatest position in the Representationsuch that, for each media component contained in the Representation, allaccess units with presentation time greater than or equal to T_(RAP) canbe correctly decoded using data in the Representation starting atI_(RAP) and no data before I_(RAP) (preceded by initialising with theInitialisation Segment, if any).

RAPs may be used to randomly access a media presentation, for example atthe start-up of the media presentation or after a seeking operation. Inaddition, RAPs may permit switching between two representations. Forseamless switching, the switch-from representation is presented up toT_(RAP) and the switch-to representation is presented from therepresentation Access Point starting from T_(RAP).

There are obvious benefits for the client to be able to identify RAPsand one or several of their properties, in particular I_(RAP) andT_(RAP), without requiring to access data at positions followingI_(RAP). Such information may be provided explicitly in the segmentindex or at least implicitly in the MPD by using the flags@startWithRAP, @segmentAlignment, and @subSegmentAlignment.

A Component Access Point (CAP) for a particular media component in arepresentation is defined as a position in the representation that isidentified as being a position for which it is possible to startplayback that media component using only the information contained indata in the Representation starting from that position onwards (precededby initializing with the Initialization Segment, if any).

In an embodiment, each CAP is associated with five properties, I_(CAP),T_(CAP), P_(RAP), X_(RAP), and Y_(RAP). T_(CAP) is the earliestpresentation time such that all access units of the media component withpresentation time greater than or equal to T_(CAP) can be correctlydecoded using data in the representation starting at I_(CAP) and no databefore I_(CAP) (preceded by initialising with the initialisationsegment, if any). I_(CAP) is the greatest position in the representationsuch that all access units of the media component with presentation timegreater than or equal to T_(CAP) can be correctly decoded using data inthe representation starting at I_(CAP) and no data before I_(CAP)(preceded by initialising with the initialisation segment, if any).

P_(CAP) is the earliest presentation time of any access unit of themedia component that can be correctly decoded using data in therepresentation starting at I_(CAP) and no data before I_(CAP) (precededby initialising with the Initialisation Segment, if any). X_(CAP) is theearliest presentation time of any access unit of the media component indata in the representation starting at I_(CAP). Y_(CAP) is thepresentation time of the first access unit of the reference stream indecoding order in data in the representation starting at I_(CAP). In anembodiment, for any RAP associated with a particular pair of I_(RAP) andT_(RAP) in a representation that contains one or more than one mediacomponent, the following statements are applicable: At least one of themedia components contains a CAP for which the I_(CAP) is equal to theI_(RAP); at least one of the media components contains a CAP for whichthe T_(CAP) is equal to the T_(RAP); and each of the media componentscontains a CAP for which the I_(CAP) is equal to or greater than theI_(RAP) and the T_(CAP) is equal to or less than the T_(RAP).

In an embodiment, four types of CAP may be defined as follows:

Type 1: X_(CAP)=P_(CAP)=T_(CAP)=Y_(CAP);

Type 2: X_(CAP)=P_(CAP)=T_(CAP)<Y_(CAP);

Type 3: X_(CAP)<P_(CAP)=T_(CAP); and

Type 4: X_(CAP)<=P_(CAP)<T_(CAP).

It is noted that the type of CAP is dependent only on which Access Unitsare decodable and their arrangement in presentation order. Type 1corresponds to what is known in some coding schemes as a “Closed-GoPrandom access point,” in which all access units, in decoding order,starting from I_(CAP) can be correctly decoded, resulting in acontinuous time sequence of decoded access units with no gaps. Here, thefirst access unit in decoding order in the reference stream startingfrom I_(CAP) is also the first access unit in presentation order. Type 2corresponds to what is known in some coding schemes as a “Closed-GoPrandom access point” wherein the first access unit in decoding order inthe reference stream starting from I_(CAP) is not the first access unitin presentation order.

Type 3 corresponds to what is known in some coding schemes as an“Open-GoP random access point” or a “Gradual Decoding Refresh (GDR)random access point,” in which there are some access units in decodingorder in the reference stream starting from I_(CAP) that cannot becorrectly decoded and these access units have presentation times lessthan T_(CAP). Type 4 corresponds to the case wherein there is at leastone access unit in decoding order in the reference stream starting fromI_(CAP) that cannot be correctly decoded and has a presentation timegreater than T_(CAP).

In some embodiments, CAPs may coincide with random access points in thestream of the media component.

FIG. 2c represents a particular multiplexed representation that containsa video stream and an audio stream. Each index number represents adecodable subsegment. Annotated subsegments that are independentlydecodable are labeled, while subsegments that are not independentlydecodable (i.e. that require decoding previous segments) are left blank.Since both video and audio segments at indexes 1 and 9 are independentlydecodable, indexes 1 and 9 represent RAPs. Video subsegments at indexes3 and 7 are independently decodable, but the audio subsegments at theseindexes are not decodable, therefore Video subsegments at indexes 3 and7 represent CAPs. Similarly, Audio subsegment and index 5 isindependently decodable, while the video subsegment at this index isnot. Therefore, the audio subsegment at index 5 is a CAP. In someembodiments, the individual video and audio subsegments at indexes 1 and9 may also be considered CAPs. It should be appreciated that the examplemultiplexed representation of FIG. 2C is just one example of amultiplexed representation and its relationship to RAPs and CAPs. Inalternative embodiments of the present invention actual multiplexedrepresentations may have more components and greater or fewersubsegments representing various types of streaming media.

Table 1 outlines the Semantics of common attributes and elements thatmay be provided in a media presentation description (MPD). In oneembodiment, URLs may be used, for example, as specified in sub-clause5.4.4 in MPEG output document W11930 (v2), and representations may beused as specified in sub-clause 5.4.2. Alternatively, other URL andrepresentation definitions may be used.

TABLE 1 Semantics of common attributes and elements are provided inElement or Attribute Name Use Description Common attributes and elements@width O specifies the horizontal visual presentation size of the videomedia type on a square grid determined by the @parx and @paryattributes. @height O specifies the vertical visual presentation size ofthe video media type, on a square grid determined by the @parx and @paryattributes. This value should be equal to the vertical pixel resolutionof the video. @parx O specifies the horizontal size of the encoded videopixels (samples) (in arbitrary units). The default value is 1. @pary Ospecifies the vertical size of the encoded video pixels (in the samearbitrary units as @parx). The default value is 1. @frameRate Ospecifies the output frame rate or the output field rate of the videomedia type in the Representation for progressive or interlaced video,respectively. If the frame or field rate is varying, the value is theaverage frame or field rate over the entire duration of theRepresentation. In case of a multiview complementary Representation, thevalue indicates the frame or field rate of a single view. @lang Ospecifies the language code(s) for this Representation. Note, multiplelanguage codes may be declared as a white-space separated list andindicate that the Representation may suit a preference for any of theindicated languages. For a full indication of what media is offeredunder each language, the Initialisation Segment or a Media Segment mayhave to be accessed. @numberOfChannels O specifies the number of audiooutput channels or a list of available audio channels. For example,@numberOfChannels=”5.1 2” for an MPEG Surround Representation@samplingRate O A single value specifying the sample rate of the audiostream or a list of sample rates available in the audio stream, e.g.@samplingRate=”44100 22050” for an HE-AAC stream with the SBR toolenabled and backwards compatible signalling. @mimeType must be specifiesthe MIME type of the Initialisation Segment, if present on at present;if the Initialisation Segment is not present it least one provides theMIME type of the first Media Segment. hierarchy level @codecs must bespecifies the codecs parameter specifying the media present on at typeswithin the Representation. least one hierarchy level @group O specifiesthe Group. @maximumRAPPeriod O When present, specifies the maximum timeinterval between the T_(RAP) of any two successive RAPs in seconds inthis Representation. @startWithRAP O When present and greater than 0,specifies that, in the associated Representations, each media componentstarts with a CAP in each Media Segment, and the first CAP for eachmedia component in each Media Segment is of a type less than or equal tothe value of this attribute. @maxPlayoutRate O specifies the maximumplayout rate as a multiple of the regular playout rate, which issupported with the same decoder profile and level requirements as thenormal playout rate. @codingDependency O When present and ‘true’, forall media types, specifies that there is at least one access unit thatdepends on one or more other access units for decoding. When present and‘false’, for any media type, there is no access unit that depends on anyother access unit for decoding (e.g. for video all the pictures areintra coded). When not present, there may or may not be codingdependency between access units. ContentProtection 0 . . . N specifiesinformation about content protection schemes used for thisRepresentation or Group of Representation. When not present the contentis neither encrypted nor DRM protected. When multiple elements arepresent, then the successful processing of one of the elements issufficient to access the described Representations. Accessibility 0 . .. N specifies information about Accessibility Information scheme Rating0 . . . N specifies information Content rating scheme Viewpoint 0 . . .N specifies information Content View Point annotation schemeMultipleViews 0 . . . 1 specifies information for video that containsmultiple views Legend: For attributes: M = Mandatory, O = Optional, OD =Optional with Default Value, CM = Conditionally Mandatory. For elements:<minOccurs> . . . <maxOccurs> (N = unbounded) Elements are bold;attributes are non-bold and preceded with an @.

If @startWithRAP is present and the value is greater than 0, thefollowing applies in the case of an ISO base media file format: (1) Inthe associated representations, each media component starts with a CAPin each Media Segment, and the first CAP for each media component ineach Media Segment is of a type less than or equal to the value of thisattribute; (2) If the value of the attribute is equal to 1 or 2, thefirst access unit in each media component in each Media Segment can bemarked as a sync sample by the sync sample table box when present, theabsence of the sync sample table box, or the matching indicator in themovie fragment; and (3) If the value of the attribute is equal to 3, thefirst access unit in each media component in each Media Segment can bemarked as a member of a sample group of type ‘rap’, or as a member of asample group of type ‘roll’ wherein the value of the roll_distance fieldis greater than 0.

In an embodiment, the XML syntax of common attributes and elements areprovided in Table 2.

TABLE 2 XML Syntax of Common Attributes and Elements<!-RepresentationBase type; extended by other Representation-relatedtypes → <xs:complexType name=”RepresentationBaseType”> <xs:sequence><xs:element name=”ContentProtection” type=”ContentDescriptorType”minOccurs=”0” maxOccurs=”unbounded”/> <xs:element name=”Accessibility”type=”ContentDescriptorType” minOccurs=”0” maxOccurs=”unbounded”/><xs:element name=”Rating” type=”ContentDescriptorType” minOccurs=”0”maxOccurs=”unbounded”/> <xs:element name=”Viewpoint”type=”ContentDescriptorType” minOccurs=”0” maxOccurs=”unbounded”/><xs:element name=”MultipleViews” type=”MultipleViewsType”minOccurs=”0”/> <xs:any namespace=”##other” processContents=”lax”minOccurs=”0” maxOccurs=”unbounded”/> </xs:sequence> <xs:attributename=”Group” type=”xs:unsignedInt”/> <xs:attribute name=”width”type=”xs:unsignedInt”/> <xs:attribute name=”height”type=”xs:unsignedInt”/> <xs:attribute name=”parx”type=”xs:unsignedInt”/> <xs:attribute name=”pary”type=”xs:unsignedInt”/> <xs:attribute name=”lang”type=”LangVectorType”/> <xs:attribute name=”mimeType” type=”xs:string”/><xs:attribute name=”codecs” type=”xs:string”/> <xs:attributename=”startWithRAP” type=”RAPtype”/> <xs:attribute name=”frameRate”type=”xs:double”/> <xs:attribute name=”maximumRAPPeriod”type=”xs:double”/> <xs:attribute name=”numberOfChannels”type=”StringVectorType”/> <xs:attribute name=”samplingRate”type=”StringVectorType”/> <xs:attribute name=”maxPlayoutRate”type=”double”/> <xs:attribute name=”codingDependency” type=”xs:oolean”/> <xs:anyAttribute namespace=”##other” processContents=”lax”/></xs:complexType> <!-Type for space delimited list of strings →<xs:simpleType name=”StringVectorType “> <xs:list itemType=”xs:string”/></xs:simpleType> <!-Type for space delimited list of language codes →<xs:simpleType name=”LangVectorType”> <xs:list itemType=”xs:language”/></xs:simpleType> <xs:simpleType name=”RAPtype”> <xs:restrictionbase=”xs:unsignedInt”>  <xs:minInclusive value=”0”/>  <xs:maxInclusivevalue=”4”/> </xs:restriction> </xs:simpleType>

In some embodiments, a segment index or metadata may be included with asegment. In an embodiment, a Segment Index Box can be defined asfollows:

-   -   Box Type: ‘sidx’    -   Container: File    -   Mandatory: No    -   Quantity: Zero or more

The Segment Index box (‘sidx’) provides a compact index of the mediasegment to which it applies. In some embodiments, the segment index boxmay be used not only with media formats based on this specification(i.e. files containing sample tables and movie fragments), but alsoother media formats (for example, MPEG-2 Transport Streams). For thisreason, the formal description of the box given here is generic.Furthermore, specific definitions for segments using movie fragments arealso given.

Each Segment Index box documents a subsegment, which is defined as atime interval of a segment, ending either at the end of the containingsegment, or at the beginning of a subsegment documented by anotherSegment Index box. A Segment Index box defines how a subsegment isdivided into one or more subsegments. In an embodiment, the subsegments,themselves, may be further subdivided using Segment Index boxes.

The indexing may refer directly to the media bytes of a subsegment, orto segment indexes which (directly or indirectly) refer to the mediabytes of subsegments. In an embodiment, the segment index may bespecified in a ‘hierarchical’ or ‘daisy-chain’ or other form bydocumenting time and byte offset information for other Segment Indexboxes applying to the same segment or subsegment.

In Media Segments (i.e., not an Initialization Segment containing onlyinitialization information), the first Segment Index box may document asubsegment that is the entire segment.

Segment Index boxes may be inline in the same file as the indexed mediaor, in some cases, out-of-line (an index segment, or ‘side file’)containing only indexing information in some embodiments.

In an embodiment, a Segment Index box contains a sequence of referencesto subsegments of the subsegment documented by the box. The referencedsubsegments are contiguous in presentation time. Similarly, the bytesreferred to by a Segment Index box are always contiguous in both themedia file and the out-of-line index segment, or in the single file ifindexes are placed within the media file. The referenced size gives thecount of the number of bytes in the material referenced.

In the file containing the Segment Index box, the anchor point for aSegment Index box is the first byte after that box. If there are twofiles, the anchor point in the media file is the beginning of thetop-level segment (i.e. the beginning of the segment file if eachsegment is stored in a separate file). The material in the filecontaining media (which may be the integrated file) starts at theindicated offset from the anchor point. If there are two files, thematerial in the index file starts at the anchor point, i.e. immediatelyfollowing the Segment Index box.

One track or stream in the segment (normally a track or stream in whichnot every sample is independently coded, such as video) is selected as areference track or stream. The earliest presentation time of thereference track or stream of each referenced subsegment is documented inthe Segment Index box. Each reference contains a reference type thatdefines whether the reference refers directly to the media data of thereferenced subsegment or to a Segment Index (‘sidx’) Box for thereferenced subsegment.

Within the two constraints that (1) in time, the subsegments arecontiguous in time, that is, each entry in the loop is consecutive fromthe immediately preceding one and (2) within a given file (integratedfile, media file, or index side file) the referenced bytes arecontiguous, there are a number of possibilities:

1) A reference to a segment index box may include, in its byte count,immediately following Segment Index boxes that document subsegments;

2) In an integrated file, using the first_offset field, Segment Indexboxes are separate from the media to which they refer;

3) In an integrated file, Segment Index boxes for subsegments arelocated close to the media they index; and

4) When a separate out-of-line index segment is used, loop entries areof a “mixed type;” some to Segment Index boxes in the index segment, andsome to media subsegments in the media file.

It is noted that profiles may be used to restrict the placement ofsegment indexes, or the overall complexity of the indexing.

In an embodiment, the earliest presentation time (for the referencetrack or stream) of the first subsegment documented in the index isexplicitly given. For each subsegment, a subsegment duration isprovided. The earliest presentation time of a subsegment may becalculated by summing the subsegment durations of the precedingsubsegments and the earliest presentation time of the first subsegment.The earliest presentation time of a subsegment is the earliestpresentation time on the reference track timescale of any sample in thereference track of the subsegment.

In an embodiment, a Segment Index box contains a Representation AccessPoint (RAP) if any entry in the loop contains a RAP.

For files based on ISO base media file format (i.e. based on moviesample tables and movie fragments): (1) a subsegment is a self-containedset of one or more consecutive movie fragments; a self-contained setcontains one or more movie fragment boxes with the corresponding mediadata box(es), and each movie fragment box immediately precedes itscorresponding media data box; (2) Segment index boxes are be placedbefore subsegment material, that is, before any Movie Fragment (‘moof’)box; (3) streams are tracks in the file format, and stream IDs are trackIDs; and presentation times are composition times.

In an embodiment, the syntax for a segment index box may be described asfollows:

aligned(8) class SegmentIndexBox extends FullBox(‘sidx’, version, 0) {unsigned int(32) reference_ID; unsigned int(32) timescale; if(version==0) { unsigned int(32) earliest_presentation_time; unsignedint(32) first_offset; } else { unsigned int(64)earliest_presentation_time; unsigned int(64) first_offset; } unsignedint(16) reserved = 0; unsigned int(16) reference_count; for(i=1; i <=reference_count; i++) { bit (1) reference_type; unsigned int(31)referenced_size; unsigned int(32) subsegment_duration; bit(1)contains_RAP; unsigned int(31) RAP_delta_time; } }

The semantics for the above syntax may be provided as follows:

reference_ID provides the stream ID for the reference stream

timescale provides the timescale, in ticks per second, for the time andduration fields within this box; in some embodiments, this may match thetimescale of the reference stream or track, such as the timescale fieldof the Media Header Box of the track.

earliest_presentation_time is the earliest presentation time of anysample in the reference stream in the first subsegment, in the timescaleindicated in the timescale field;

first_offset is the distance in bytes, in the file containing media,from the anchor point, to the first byte of the indexed material;

reference_count provides the number of referenced items;

reference_type: when set to 1 indicates that the reference is to asegment index (‘sidx’) box; otherwise the reference is to media content(e.g., in the case of files based on this specification, to a moviefragment box); if a separate index segment is used, then entries withreference type 1 are in the index segment, and entries with referencetype 0 are in the media file;

referenced_size: the distance in bytes from the first byte of thereferenced item to the first byte of the next referenced item, or in thecase of the last entry, the end of the referenced material;

subsegment_duration: when the reference is to Segment Index box, thisfield carries the sum of the subsegment_duration fields in that box;when the reference is to a subsegment, this field carries the differencebetween the earliest presentation time of any sample of the referencestream in the next subsegment (or the first subsegment of the nextsegment, if this is the last subsegment of the segment or the endpresentation time of the reference stream if this is the last subsegmentof in the reference stream) and the earliest presentation time of anysample of the reference stream in the referenced subsegment; theduration is in the same units as earliest_presentation_time;

contains_RAP: this bit shall be 1 if the referenced material contains atleast one RAP; otherwise this bit is set to 0. In other words, when thereference is to a subsegment, then this bit shall be 1 if the subsegmentcontains at least one RAP, otherwise this bit is set to 0; when thereference is to a segment index, then this bit shall be set to 1 only ifany of the references in that segment index have this bit set to 1, and0 otherwise;

RAP_delta_time: if contains_RAP is 1, provides information on theT_(RAP) of the first RAP in the referenced material; reserved with thevalue 0 if contains_RAP is 0. The time is expressed as the differencebetween the T_(RAP) of the first RAP in the referenced material and theearliest_presentation_time field;

In an alternative embodiment, a Segment Index Box may be defined asfollows:

-   -   Box Type: ‘sidx’    -   Container: File    -   Mandatory: No    -   Quantity: Zero or more

The Segment Index box (‘sidx’) provides a compact index of the mediasegment to which it applies. It is designed so that it can be used notonly with media formats based on this specification (i.e. filescontaining sample tables and movie fragments), but also other mediaformats (for example, MPEG-2 Transport Streams). For this reason, theformal description of the box given here is deliberately generic, andthe specific definitions for segments using movie fragments are alsogiven.

Each Segment Index box documents a subsegment, which is defined as atime interval of a segment, ending either at the end of the containingsegment, or at the beginning of a subsegment documented by anotherSegment Index box. A Segment Index box defines how a subsegment isdivided into one or more subsegments (which may themselves be furthersubdivided using Segment Index boxes).

The indexing may refer directly to the media bytes of a subsegment, orto segment indexes which (directly or indirectly) refer to the mediabytes of subsegments; the segment index may be specified in a‘hierarchical’ or ‘daisy-chain’ or other form by documenting time andbyte offset information for other Segment Index boxes applying to thesame segment or subsegment.

In Media Segments (i.e., not an Initialisation Segment containing onlyinitialization information), the first Segment Index box documents asubsegment that is the entire segment.

Segment Index boxes may be inline in the same file as the indexed mediaor, in some cases, out-of-line (an index segment, or ‘side file’)containing only indexing information.

A Segment Index box contains a sequence of references to subsegments ofthe subsegment documented by the box. The referenced subsegments arecontiguous in presentation time. Similarly, the bytes referred to by aSegment Index box are always contiguous in both the media file and theout-of-line index segment, or in the single file if indexes are placedwithin the media file. The referenced size gives the count of the numberof bytes in the material referenced.

In the file containing the embodiment Segment Index box, the anchorpoint for a Segment Index box is the first byte after that box. If thereare two files, the anchor point in the media file is the beginning ofthe top-level segment (i.e., the beginning of the segment file if eachsegment is stored in a separate file). The material in the filecontaining media (which may be the integrated file) starts at theindicated offset from the anchor point. If there are two files, thematerial in the index file starts at the anchor point, i.e. immediatelyfollowing the Segment Index box.

One track or stream in the segment (normally a track or stream in whichnot every sample is independently coded, such as video) is selected as areference track or stream. If there are also other tracks or streams inthe segment for which not every sample is independently coded, thenthose other tracks or streams are selected as additional referencetracks or streams.

The earliest presentation time of the reference track or stream of eachreferenced subsegment is documented in the Segment Index box. Eachreference contains a reference type that defines whether the referencerefers directly to the media data of the referenced subsegment or to aSegment Index (‘sidx’) Box for the referenced subsegment.

Within the two constraints (1) that, in time, the subsegments arecontiguous, that is, each entry in the i-loop is consecutive from theimmediately preceding one and (2) within a given file (integrated file,media file, or index side file) the referenced bytes are contiguous,there are a number of possibilities.

1) a reference to a segment index box may include, in its byte count,immediately following Segment Index boxes that document subsegments;

2) In an integrated file, using the first_offset field, Segment Indexboxes are separate from the media to which they refer;

3) In an integrated file, Segment Index boxes for subsegments arelocated close to the media they index;

4) When a separate out-of-line index segment is used, the i-loop entriesare of “mixed type:” some to Segment Index boxes in the index segment,and some to media subsegments in the media file.

It is noted that profiles may be used to restrict the placement ofsegment indexes, or the overall complexity of the indexing.

The earliest presentation time (for the reference track or stream) ofthe first subsegment documented in the index is explicitly given. Foreach subsegment, a subsegment duration is provided. The earliestpresentation time of a subsegment may be calculated by summing thesubsegment durations of the preceding subsegments and the earliestpresentation time of the first subsegment. The earliest presentationtime of a subsegment is the earliest presentation time on the referencetrack timescale of any sample in the reference track of the subsegment.

A Segment Index box contains a Component Access Point (CAP) for thereference stream or an additional reference stream if any entry in thei-loop contains a CAP for the reference stream or an additionalreference stream.

For files based on ISO base media file format (i.e. based on moviesample tables and movie fragments): (1) a subsegment is a self-containedset of one or more consecutive movie fragments; a self-contained setcontains one or more movie fragment boxes with the corresponding mediadata box(es), and each movie fragment box immediately precedes itscorresponding media data box; (2) Segment Index boxes are placed beforesubsegment material, that is, before any Movie Fragment (‘moof’) box;(3) streams are tracks in the file format, and stream IDs are track IDs;and (4) presentation times are composition times.

The syntax of the alternative embodiment segment index box be describedas follows:

aligned(8) class SegmentIndexBox extends FullBox(‘sidx’, version, 0) {unsigned int(32) reference_ID; unsigned int(32) timescale; if(version==0) { unsigned int(32) earliest_presentation_time; unsignedint(32) first_offset; } Else { unsigned int(64)earliest_presentation_time; unsigned int(64) first_offset; } unsignedint(8) reserved = 0; unsigned int(16) reference_count; unsigned int(8)num_additional_reference_IDs; for(k=1; k <=num_additional_reference_IDs; k++) { unsigned int(32)additional_reference_ID[k]; } for(i=1; i <= reference_count; i++) { bit(1) reference_type; unsigned int(31) referenced_size; unsigned int (32)subsegment_duration; for(j=0; j <= num_additional_reference_IDs; j++) {bit(1) contains_RAP[j]; unsigned int(31) RAP_delta_time[j]; } } }

In the alternate embodiment, the semantics may be provided as follows:

reference_ID provides the stream ID for the reference stream

timescale provides the timescale, in ticks per second, for the time andduration fields within this box; it is recommended that this match thetimescale of the reference stream or track; for files based on thisspecification, that is the timescale field of the Media Header Box ofthe track;

earliest_presentation_time is the earliest presentation time of anysample in the reference stream in the first subsegment, in the timescaleindicated in the timescale field;

first_offset is the distance in bytes, in the file containing media,from the anchor point, to the first byte of the indexed material;

reference_count provides the number of referenced items;

num_additional_reference_IDs provides the number of additional referencestreams;

additional_reference_ID [k] provides the stream ID for the k-thadditional reference stream;

reference_type: when set to 1 indicates that the reference is to asegment index (‘sidx’) box; otherwise the reference is to media content(e.g., in the case of files based on this specification, to a moviefragment box); if a separate index segment is used, then entries withreference type 1 are in the index segment, and entries with referencetype 0 are in the media file;

referenced_size: the distance in bytes from the first byte of thereferenced item to the first byte of the next referenced item, or in thecase of the last entry, the end of the referenced material;

subsegment_duration: when the reference is to Segment Index box, thisfield carries the sum of the subsegment_duration fields in that box;when the reference is to a subsegment, this field carries the differencebetween the earliest presentation time of any sample of the referencestream in the next subsegment (or the first subsegment of the nextsegment, if this is the last subsegment of the segment or the endpresentation time of the reference stream if this is the last subsegmentof in the reference stream) and the earliest presentation time of anysample of the reference stream in the referenced subsegment; theduration is in the same units as earliest_presentation_time;

contains_RAP [j]: this bit shall be 1 if the referenced materialcontains at least one CAP for the reference stream (when j is equal to0) or the j-th additional reference stream (when j is greater than 0),otherwise this bit is set to 0. In other words, when the reference is toa subsegment, then this bit shall be 1 if the subsegment contains atleast one RAP for the reference stream (when j is equal to 0) or thej-th additional reference stream (when j is greater than 0), otherwisethis bit is set to 0; when the reference is to a segment index, thenthis bit shall be set to 1 only if any of the references in that segmentindex have this bit set to 1, and 0 otherwise;

RAP_delta_time [j]: if contains_RAP [j] is 1, provides information onthe T_(CAP) of the first CAP in the referenced material for thereference stream (when j is equal to 0) or the j-th additional referencestream (when j is greater than 0); reserved with the value 0 ifcontains_RAP [i] is 0. The time is expressed as the difference betweenthe T_(CAP) of the first CAP in the referenced material for thereference stream (when j is equal to 0) or the j-th additional referencestream (when j is greater than 0) and the earliest_presentation_timefield.

FIGS. 3-5 illustrate flowcharts depicting example embodiment streamingoperations. It should be understood that these figures depict specificexamples of many possible embodiment methods. FIG. 3a illustrates a flowdiagram of operations 300 in displaying streamed media content.Operations 300 may be indicative of operations occurring in a subscriberas the subscriber displays streamed media content.

Operations 300 may begin with the subscriber or client establishing amedia content stream (or connection) with a server (block 302). Theconnection may or may not be a persistent connection between thesubscriber and the server. The subscriber may start to establish themedia content stream with the server by sending a request to the server.Such a request may be an HTTP GET request containing the URL of themanifest for the media content, for example. Part of the establishmentof the media content stream may be a setting of a variety of parametersof the media content stream, including spatial resolution, bitrate,frame rate, content extras, advertisement level, and so forth. Theparameters may be based on the subscriber's subscription level,available communications system bandwidth, operation conditions, and soforth.

In step 304, the client receives information on multiplexedrepresentations and component access points. In an embodiment theinformation on multiplexed representations may be contained in amanifest file such as an MPD file for a HTTP streaming. In someembodiments component access points may be listed or indexed in asegment index box that is contained in an independent file or containedin the same streaming file as the particular multiplexed representationrequested by the client. In step 306, the client selects a firstmultiplexed representation and initial access points. The selection ofthe first multiplexed representation may be dependent on the client'snetwork performance, such as bandwidth and quality of service, and theclient's preference with respect to language and video resolution. Thesepreferences may be stored in a user setup file on the client, areselected by user correctly. In an embodiment, the initial access pointsmay correspond to a RAP and/or CAP listed in the manifest file and orand index.

Once the multiplexed representation and initial access points aredetermined, the client requests media content corresponding to the firstmultiplexed representation as shown in step 308. In an embodiment, thisrequest may comprise submitting a URL of the first multiplexedrepresentation along with an index that corresponds with the initialaccess points. In step 310, the client receives the media contentcorresponding to the first multiplexed representation, and the receivedmedia content is displayed in step 312.

In an embodiment, the client may decide to switch its multiplexedrepresentation from the first multiplexed representation to a secondmultiplexed representation (step 314). Such a change in multiplexedrepresentation may occur, for example, if there is a change in networkperformance that would warrant a switching video streams. For example,if the client detects a decrease in available network bandwidth, theclient may want to switch video streams from a high-bandwidth videostream to a low bandwidth video stream. In other situations, the clientmay switch audio streams from a first language to a second languagebased on user input. Of course, these are only examples of the manyreasons why a client would want to switch a particular representation.Because the various representations are multiplexed, switching at leastone stream entails changing from the first multiplexed representation toa second multiplexed representation that corresponds to the particularcomponents required by the client.

In step 316 the client requests media content of the second multiplexedrepresentation. In this step, the client may access a subsegment of astreaming file corresponding to the second multiplexed representation ata subsegment that corresponds with a CAP or RAP defined in the manifestor index in an embodiment. In some embodiments, the access point isdetermined in such a way that the transition from streaming the firstmultiplexed representation to the second multiplexed representation isperformed in a seamless fashion. By directly accessing an access pointbased on the CAP or RAP, the transition in representations may beaccomplished quickly and efficiently such that the next decodablesubsegment is directly accessed without having to search through ordownload on decodable subsegments. In step 318, the client displays themedia content of the second multiplexed representation.

FIG. 3b illustrates a flow diagram of streaming media content operations350. Operations 350 may be indicative of operations occurring in aserver as the server streams media content to a client or subscriber.Operations 350 may begin with the server establishing a media contentstream with the subscriber (block 352). The server may establish themedia content stream with the subscriber after receiving a request fromthe subscriber to establish the media content stream with thesubscriber. Part of the establishment of the media content stream may bea setting of a variety of parameters of the media content stream,including spatial resolution, bitrate, frame rate, content extras,advertisement level, and so forth. The parameters may be based on thesubscriber's subscription level, available communications systembandwidth, operation conditions, and so forth.

According to an example embodiment, the server may send information onmultiplexed representations and component access points to the client(step 354). After the server receives a media content request based onthe multiplexed representation and access points (step 356), the serverstreams media content (step 358).

FIG. 4a illustrates client operations 400 according to anotherembodiment of the present invention. In step 402, the client establishesa media content stream. In an embodiment, this media content stream maybe established by sending a URL request for a manifest or an MPD. Instep 404, the client receives the manifest, and selects a multiplexedrepresentation and access points based on data in the manifest accordingto embodiments described herein in step 406. In step 408, the clientsends a request for the selected multiplexed representation according tothe selected access points, and receives the media content in step 410.The client then displays the content (step 412). In an embodiment, theclient may switch multiplexed views from the originally selectedmultiplexed representation to a further multiplexed representationaccording to client requirements and network performance, as an example.

FIG. 4b illustrates server operations according to another embodiment ofthe present invention. In step 452, this server establishes a mediacontent stream. In an embodiment this media content stream isestablished upon reception of a URL request for an MPD or manifest file.In step 454 the server sends the manifest file to the client, and instep 456 the server receives a media content request for a particularmultiplexed representation according to an access point. The server thenstreams the media content to the client in step 458.

FIG. 5A illustrates client operations 500 according to a furtherembodiment of the present invention. In step 502, the client establishesa media content stream with a server. In step 504, the client receives amanifest, such as an MPD from the server. In an embodiment this manifestcontains information regarding multiplexed views and types of accesspoints, such as component access points and/or representation accesspoints according to embodiments described herein. Based on theinformation in the manifest, the client selects a first multiplexedrepresentation in step 506. In step 508, the client receives an index ofthe first multiplexed representation. In an embodiment this index may becontained in a separate file or it may be attached to the same streamingfile as the requested segment of the first multiplexed representation.In one embodiment this index may be in the form of a segment index box.

In step 510, the client selects a subsegment of the first multiplexedrepresentation based on the RAPs and CAPs listed in the index. Next, arequest for the particular subsegment of the first multiplexedrepresentation is sent in step 512, and the content is received from theserver in step 514. In step 516 the client plays the content of thefirst multiplexed representation.

In step 518, the client may select a second multiplexed representationbased on data listed in the manifest. As described above, this electionmay be based on network conditions and/or user input. In step 520 anindex of the second multiplexed representation is received, and asubsegment of the second multiplexed representation is selected based oncomponent access points in the index in step 522. A request for thissubsegment of the second multiplexed representation is sent in step 524,the content is received in step 526, and the content of the secondmultiplexed representation is played in step 528. As described above, insome embodiments, the transition from the first multiplexedrepresentation to the second multiplexed representation is a seamlesstransition. One way in which such a seamless transition is affected isdue to the fact that the changeover from the first multiplexedrepresentation to the second multiplexed representation is efficientbecause the first decodable subsegment for a particular presentationtime is directly accessed without having to access a decodable accesspoints.

FIG. 5b illustrates server operations 500 according to an alternativeembodiment of the present invention. In step 552 the server establishesa media content stream with a client, and in step 554 the server sends amanifest to the client. As described above, this manifest containsinformation about various multiplexed representations as well asinformation regarding CAPs and RAPs. In step 556 the server sends andindex of CAPs and/or RAPs to the client. In one embodiment, this indexis based on a selected multiplexed representation and may be attached toa multiplexed streaming segment file. Alternatively this index may be anindependent file requested by the client. In step 558, the serverreceives a media content request from the client based on a selectedmultiplexed representation and access point selected by the client. Thisrequest may be in the form of a URL in the case of HTTP streaming. Instep 560, the server streams the selected media content to the client.

FIG. 6 illustrates computer system 600 adapted to use embodiments of thepresent invention, e.g., storing and/or executing software associatedwith the embodiments. Central processing unit (CPU) 601 is coupled tosystem bus 602. CPU 601 may be any general purpose CPU. However,embodiments of the present invention are not restricted by thearchitecture of CPU 601 as long as CPU 601 supports the inventiveoperations as described herein. Bus 602 is coupled to random accessmemory (RAM) 603, which may be SRAM, DRAM, or SDRAM. ROM 604 is alsocoupled to bus 602, which may be PROM, EPROM, or EEPROM. RAM 603 and ROM404 hold user and system data and programs as is well known in the art.

Bus 602 is also coupled to input/output (I/O) adapter 605,communications adapter 611, user interface 608, and multimedia adaptor609. The I/O adapter 605 connects storage devices 606, such as one ormore of a hard drive, a CD drive, a floppy disk drive, a tape drive, tocomputer system 600. The I/O adapter 605 is also connected to a printer(not shown), which would allow the system to print paper copies ofinformation such as documents, photographs, articles, and the like. Notethat the printer may be a printer, e.g., inkjet, laser, and the like, afax machine, scanner, or a copier machine. User interface adaptor 608 iscoupled to keyboard 613 and mouse 607, as well as other devices, andcommunications adaptor 611 is coupled to network 612 from whichembodiment media files may be received. Multimedia adapter 609, whichcan be a display and/or audio card in some embodiments, is connected todisplay device 610 and audio device 615. Display device 610 can be aCRT, flat panel display, or other type of display device, and audiodevice 615 can be a loudspeaker, headphones, or other analog or digitalaudio system.

FIG. 7 illustrates further processing system 700 that can be utilized toimplement methods of the present invention. In this case, the mainprocessing is performed in processor 702, which can be a microprocessor,digital signal processor or any other appropriate processing device.Program code (e.g., the code implementing the algorithms disclosedabove) and data can be stored in memory 704. The memory can be localmemory such as DRAM or mass storage such as a hard drive, optical driveor other storage (which may be local or remote). While the memory isillustrated functionally with a single block, it is understood that oneor more hardware blocks can be used to implement this function.

In one embodiment, the processor can be used to implement various ones(or all) of the functions discussed above. For example, the processorcan serve as a specific functional unit at different times to implementthe subtasks involved in performing the techniques of the presentinvention. Alternatively, different hardware blocks (e.g., the same asor different than the processor) can be used to perform differentfunctions. In other embodiments, some subtasks are performed by theprocessor while others are performed using a separate circuitry.

FIG. 7 also illustrates I/O port 706, which can be used to provide thevideo to and from the processor. Video source 708 (the destination isnot explicitly shown) is illustrated in dashed lines to indicate that itis not necessary part of the system. For example, the source can belinked to the system by a network such as the Internet or by localinterfaces (e.g., a USB or LAN interface).

In accordance with an embodiment, a method of operating a streamingmedia client includes electronically receiving, from a network,information regarding component access points of the first multiplexedrepresentation of a streaming content. In some embodiments, thismultiplexed representation may be included in a streaming file. Thefirst multiplexed representation of the streaming content includes aplurality of media components, and each component access point definesan independently coded access point for one of the plurality of mediacomponents. The method further includes selecting a first segment orsubsegment of the first multiplexed representation of the streamingcontent based on the information regarding the component access points,and requesting the selected first segment or subsegment of the firstmultiplexed representation of the streaming content from the network.

In an embodiment, the method also includes receiving the first segmentor subsegment from the network, and playing back the requested firstsegment or subsegment. Electronically receiving information regardingcomponent access points may also include receiving a manifest from aserver, where the manifest identifies a component access point and mayinclude a media presentation description (MPD). In some embodiments, thecomponent access point type indicates whether access units of a mediacomponent following a particular component access point are alldecodable and/or whether access units of the media component follow theparticular component access point in presentation order. Moreover,electronically receiving information regarding component access pointsmay also receiving an index of component access points of the firstmultiplexed representation of the streaming content. In someembodiments, this index may be in the form of a segment index box.

In an embodiment, a first plurality of the media components includes avideo component, and a second of the plurality of media componentsincludes an audio component.

In an embodiment, the method also includes changing requesting segmentsor subsegments from the first multiplexed representation of thestreaming content to a second multiplexed representation of thestreaming content. Changing multiplexed representations may includeselecting a second segment or subsegment of a second multiplexedrepresentation of the streaming content based on the electronicallyreceived information regarding component access points, requesting theselected second segment or subsegment of the second multiplexedrepresentation of the streaming content, and receiving the requestedsecond segment or subsegment from the network. The first multiplexedrepresentation may include a first version of a first media component,and a first version of a second media component; and the secondmultiplexed representation may include the first version of the firstmedia component and a second version of the second media component. Thefirst version of the first media component may be an audio component,the first version of the second media component may be a video componentat a first video resolution or a first bit rate, and the second versionof the second media component may be the video component at a secondvideo resolution or a second bit rate. In some embodiments, the methodmay also include determining whether to change multiplexedrepresentations based on network conditions or available networkresources before changing multiplexed representations of the streamingcontent. The method may further include playing back the requested firstsegment or subsegment, and playing back the requested second segment orsubsegment after playing back the requested first segment or subsegment.In some embodiments, a change from the first segment or subsegment tothe second segment or subsegment occurs seamlessly.

In accordance with a further embodiment, a method of operating astreaming media server includes electronically transmitting to a clientinformation regarding component access points of the first multiplexedrepresentation of the streaming content. The first multiplexedrepresentation of the streaming content includes a plurality of mediacomponents, and each component access point defines an independentlycoded access unit for one of the plurality of components. The methodfurther includes receiving a request from the client for a first segmentor subsegment of the first multiplexed representation of the streamingcontent according to a selected component access point, and transmittingthe requested first segment or subsegment of the first multiplexedrepresentation of the streaming content to the client.

In an embodiment, electronically transmitting information regardingcomponent access points includes transmitting a manifest to the client,where the manifest identifies a component access point type. Themanifest may include a media presentation description (MPD). In anembodiment, the component access point type indicates whether all accessunits of a media component following the component access points are alldecodable and/or whether access units following a component access pointfollow the particular component access point in presentation order. Insome embodiments, electronically transmitting information regardingcomponent access points conclusions transmitting an index of componentaccess points of the first multiplexed representation of the streamingcontent to the client.

In an embodiment a first of the plurality of media components includes avideo component, and a second of the plurality of media componentsincludes an audio component.

In an embodiment, the method also includes receiving a request from theclient for a second segment or subsegment of a second multiplexedrepresentation of the streaming content according to a further selectedcomponent access point, where the second multiplexed representation ofthe streaming content includes a second multiplexed representation ofthe plurality of media components. The method may also includetransmitting the requested second segment or subsegment of themultiplexed representation of the streaming content to the client. Thefirst multiplexed representation may include a first version of a firstmedia component and a first version of a second media component, and thesecond multiplexed representation may include the first version of thefirst media component and a second version of the second mediacomponent. In some embodiments the first version of the first mediacomponent includes an audio component, the first version of the secondmedia component includes a video component at a first video resolution,and the second version of the second media component includes the videocomponent at a second video resolution.

In accordance with a further embodiment, a system for receivingstreaming media content includes a communications adapter and aprocessor. The communication adapter receives information regardingcomponent access points of the first multiplexed representation of thestreaming content from a network, wherein the first multiplexedrepresentation of the streaming content includes a plurality of mediacomponents, and each component access point defines an independentlycoded access unit for one of the plurality of media components. Theprocessor selects a first segment or subsegment of the first multiplexedrepresentation of the streaming content based on the informationregarding the component access points, and requests the selected firstsegment or subsegment of the first multiplexed representation of thestreaming content.

In some embodiments, the system also includes a multimedia adapterconfigured to play back the first segment or subsegment of the firstmultiplexed representation of the streaming content. In an embodiment,the processor requests the selected first segment or subsegment of thefirst multiplexed representation of the streaming content by using HTTPrequests with URLs derived based on the information regarding componentaccess points.

In an embodiment, the processor further changes multiplexedrepresentations from the first multiplexed representation to a secondmultiplexed representation by selecting a second segment or subsegmentof a second multiplexed representation of the streaming content based onthe electronically received information regarding component accesspoints, and requests the selected second segment or subsegment of thesecond multiplexed representation of the streaming content from thenetwork. In an embodiment, the first multiplexed representation includesa first version of a first media component and a first version of asecond media component, and the second multiplexed representationincludes the first version of the first media component and a secondversion of the second media component. The first version of the firstmedia component may be an audio component, the first version of thesecond media component may be a video component at a first visit videoresolution or first bitrate, and the second version of the secondcomponent may be the video component at a second video resolution orsecond bitrate.

In accordance with a further embodiment, a non-transitory computerreadable medium having an executable program stored thereon thatinstructs a microprocessor to perform the steps of receiving, from anetwork, information regarding component access points of the firstmultiplexed representation of the streaming content, selecting a firstsegment or subsegment of the first multiplexed representation of thestreaming content based on the information regarding the componentaccess points, and requesting the selected first segment or subsegmentof the first multiplexed representation of the streaming content fromthe network. The first multiplexed representation of the streamingcontent includes a plurality of media components, and each componentaccess point defines an independently coded access unit for one of theplurality of components.

In an embodiment, the program further instructs the microprocessor toreceive the first selected segment or subsegment from the network andplay the received first segment or subsegment. The program may furtherinstructs the microprocessor to change multiplexed representations fromthe first multiplexed representation to a second multiplexedrepresentation by selecting a second segment or subsegment of a secondmultiplexed representation of the streaming content based on theelectronically received information regarding component access points,and requesting the selected second segment or subsegment of the secondmultiplexed representation of the streaming content. In someembodiments, the first multiplexed representation includes a firstversion of the first media component and a first version of a secondmedia component, and the second multiplexed representation includes thefirst version of the first media component and a second version of thesecond media component. The first version of the first media componentmay include an audio component, the first version of the second mediacomponent may include a video component at a first video resolution, andthe second version of the second media component may include the videocomponent at a second video resolution.

In an embodiment, the program further instructs the microprocessor toreceive the first segment or subsegment from the network, play back therequested first segment or subsegment, receive the requested secondsegment or subsegment from the network, and play back the requestedsecond segment or subsegment after playing back the requested firstsegment or subsegment.

Embodiments of the present invention provide a number of advantageousfeatures. For example, embodiments provide an improved mechanism foridentifying and signaling of media segments starting with arepresentation access point in a multiplexed representation. Embodimentsalso provide an improved mechanism for signaling of representationaccess points in media segments of a multiplexed representation. Variousembodiments also provide an improved mechanism for signaling of thepresentation time of the first representation access point in asubsegment in a media segment of a multiplexed representation.

Further advantages of some embodiments include the ability to seamlesslytransition from a first multiplexed view to a second multiplexed viewwithout delay caused by downloading access units that are undecodable orare devoted to presentation times that occur before the presentationtime at which a streaming component transitions from the first view tothe second view.

Although present embodiments and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. For example,many of the features and functions discussed above can be implemented insoftware, hardware, or firmware, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of operating a streaming media client,the method comprising: electronically receiving, from a network,information regarding component access points (CAPs) of a firstmultiplexed representation of a streaming content, wherein the firstmultiplexed representation of the streaming content comprises aplurality of media components, wherein each of the CAPs defines anindependently coded access unit for one of the plurality of mediacomponents and identifies a position in the first multiplexedrepresentation enabling playback of the respective media component usinginformation contained in data in the first multiplexed representationafter the respective CAP and independently of information in themultiplexed representation before the respective CAP, wherein each groupof CAPs of a plurality of groups of the CAPs is associated with arespective one of the plurality of media components; identifying astream access point (SAP) in the first multiplexed representation of thestreaming content based on the information regarding the CAPs, whereinthe SAP identifies a position in the first multiplexed representationenabling playback of the first multiplexed representation usinginformation contained in the first multiplexed representation startingfrom that position onwards, wherein at least one of the CAPs of eachgroup of CAPS identifies a position in the first multiplexedrepresentation that is different from the position in the firstmultiplexed representation identified by the SAP, wherein at least oneof the CAPs of each group of CAPS identifies a position in the firstmultiplexed representation that is different from positions in the firstmultiplexed representation identified by each of the CAPs in at leastone of the other ones of the plurality of groups of the CAPs, andwherein the SAP corresponds to an I_(SAP) and a T_(SAP), and wherein:the I_(SAP) is a byte position in the first multiplexed representation,and the T_(SAP) is an earliest presentation time, for any access unit ofthe media stream, that all access units of the media stream with apresentation time of at least the T_(SAP) can be correctly decoded usingthe information contained in the first multiplexed representationstarting at the I_(SAP) and no information before the I_(SAP); selectinga first segment or subsegment of the first multiplexed representation ofthe streaming content based on the SAP; and requesting the selectedfirst segment or subsegment of the first multiplexed representation ofthe streaming content from the network.
 2. The method of claim 1,further comprising: receiving the requested first segment or subsegmentfrom the network; and playing back the requested first segment orsubsegment.
 3. The method of claim 1, wherein electronically receivinginformation regarding component access points comprises receiving amanifest from a server, the manifest identifying a component accesspoint type.
 4. The method of claim 3, wherein the manifest comprises amedia presentation description (MPD).
 5. The method of claim 3, whereinthe component access point type indicates whether all access units of amedia component following a particular component access point are alldecodable.
 6. The method of claim 3, wherein the component access pointtype indicates whether all access units of a media component following aparticular component access point follow the particular component accesspoint in presentation order.
 7. The method of claim 1, whereinelectronically receiving information regarding component access pointscomprises receiving an index of component access points of a segment orsubsegment of the first multiplexed representation of the streamingcontent.
 8. The method of claim 7, wherein the index is defined by asegment index box.
 9. The method of claim 1, wherein: a first of theplurality of media components comprises a video component; and a secondof the plurality of media components comprises an audio component. 10.The method of claim 1, further comprising: changing requesting segmentsor subsegments from the first multiplexed representation of thestreaming content to a second multiplexed representation of thestreaming content, wherein changing the requesting segments orsubsegments comprises: selecting a second segment or subsegment of thesecond multiplexed representation of the streaming content based on theinformation regarding component access points, requesting the selectedsecond segment or subsegment of the second multiplexed representation ofthe streaming content, and receiving the requested second segment orsubsegment from the network.
 11. The method of claim 10, wherein: thefirst multiplexed representation of the streaming content comprises afirst version of a media first component and a first version of a secondmedia component; the second multiplexed representation of the streamingcontent comprises the first version of the first media component and asecond version of the second media component; the first version of thefirst media component comprises an audio component; the first version ofthe second media component comprises a video component at a first videoresolution or a first bitrate; and the second version of the secondcomponent comprises the video component at a second video resolution ora second bitrate.
 12. The method of claim 10, further comprising:determining whether to change multiplexed representations of thestreaming content based on network conditions or available networkresources before changing requesting segments or subsegments from thefirst multiplexed representation of the streaming content to the secondmultiplexed representation of the streaming content.
 13. The method ofclaim 10, further comprising: playing back the requested first segmentor subsegment; and playing back the requested second segment orsubsegment after playing back the requested first segment, wherein achange from the first segment or subsegment to the second segment orsubsegment occurs seamlessly.
 14. A method of operating a streamingmedia server, the method comprising: electronically transmitting, to aclient, information regarding component access points (CAPs) of a firstmultiplexed representation of a streaming content, wherein the firstmultiplexed representation of the streaming content comprises aplurality of media components, wherein each group of CAPS of a pluralityof groups of CAPs is associated with a respective one of the pluralityof the media components, wherein each of the CAPs defines anindependently coded access unit for the respective one of the pluralityof media components and identifies a position in the first multiplexedrepresentation enabling playback of the respective media component usingthe information contained in data in the first multiplexedrepresentation after the respective CAP and independently of informationin the multiplexed representation before the respective CAP, and whereinthe information regarding CAPs is configured to signal a stream accesspoint (SAP) identifying a position in the first multiplexedrepresentation enabling playback of the first multiplexed representationusing information contained in the first multiplexed representationstarting from that position onwards, wherein at least one of the CAPs ofeach group of CAPs identifies a position in the first multiplexedrepresentation that is different from the position in the firstmultiplexed representation identified by the SAP, wherein at least oneof the CAPs of each group of CAPS identifies a position in the firstmultiplexed representation that is different from positions in the firstmultiplexed representation identified by each of the CAPs in at leastone of the other ones of the plurality of groups of the CAPs, whereinthe SAP corresponds to an I_(SAP) and a T_(SAP), and wherein: theI_(SAP) is a byte position in the first multiplexed representation, andthe T_(SAP) is an earliest presentation time, for any access unit of themedia stream, that all access units of the media stream with apresentation time of at least the T_(SAP) can be correctly decoded usingthe information contained in the first multiplexed representationstarting at the I_(SAP) and no information before the I_(SAP); receivinga request from the client for a first segment or subsegment of the firstmultiplexed representation of the streaming content according to aselected CAP of the CAPS; and transmitting the requested first segmentor subsegment of the first multiplexed representation of the streamingcontent to the client.
 15. The method of claim 14, whereinelectronically transmitting information regarding component accesspoints comprises transmitting a manifest to the client, the manifestidentifying a component access point type.
 16. The method of claim 15,wherein the manifest comprises a media presentation description (MPD).17. The method of claim 15, wherein the component access point typeindicates whether all access units of a media component following thecomponent access points are all decodable.
 18. The method of claim 15,wherein the component access point type indicates whether access unitsof a media component following a particular component access pointfollow the particular component access point in presentation order. 19.The method of claim 14, wherein electronically transmitting informationregarding component access points comprises transmitting an index ofcomponent access points of the first multiplexed representation of thestreaming content to the client.
 20. The method of claim 14, wherein: afirst of the plurality of media components comprises a video component;and a second of the plurality of media components comprises an audiocomponent.
 21. The method of claim 14, further comprising: receiving arequest from the client for a second segment of subsegment of a secondmultiplexed representation of the streaming content according to afurther selected component access point, wherein the second multiplexedrepresentation of the streaming content comprises a second multiplexedrepresentation of the plurality of media components; and transmittingthe requested second segment of subsegment of the second multiplexedrepresentation of the streaming content to the client.
 22. The method ofclaim 21, wherein: the first multiplexed representation of the streamingcontent comprises a first version of a first media component and a firstversion of a media second component; the second multiplexedrepresentation of the streaming content comprises the first version ofthe first media component and a second version of the second mediacomponent; the first version of the first media component comprises anaudio component; the first version of the second media componentcomprises a video component at a first video resolution; and the secondversion of the second media component comprises the video component at asecond video resolution.
 23. A system for receiving streaming mediacontent, the system comprising: a communications adapter configured toreceive information regarding component access points (CAPs) of a firstmultiplexed representation of a streaming content from a network,wherein the first multiplexed representation of the streaming contentcomprises a plurality of media components, wherein each group of CAPs ofa plurality of groups of the CAPs is associated with a respective one ofthe plurality of the media components and each CAP defines anindependently coded access unit for the respective one of the pluralityof media components and identifies a position in the first multiplexedrepresentation enabling playback for the respective media componentusing the information contained in data in the first multiplexedrepresentation after the respective CAP and independently of informationin the multiplexed representation before the respective CAP; and aprocessor configured to identify a stream access point (SAP) in thefirst representation of the streaming content based on the informationregarding the CAPs, to select a first segment or subsegment of the firstmultiplexed representation of the streaming content based on the SAP,and to request the selected first segment or subsegment of the firstmultiplexed representation of the streaming content, wherein the SAPidentifies a position in the first multiplexed representation enablingplayback of a media stream using information contained in the firstmultiplexed representation starting from that position onwards, whereinat least one of the CAPs in each of the group of the CAPs identifies aposition in the first multiplexed representation that is different fromthe position in the first multiplexed representation identified by theSAP, wherein at least one of the CAPs of each group of CAPS identifies aposition in the first multiplexed representation that is different frompositions in the first multiplexed representation identified by each ofthe CAPs in at least one of the other ones of the plurality of groups ofthe CAPs, and wherein the SAP corresponds to I_(SAP)and a T_(SAP), andwherein: the I_(SAP) is a byte position in the first multiplexedrepresentation, and the T_(SAP) is an earliest presentation time, forany access unit of the media stream, that all access units of the mediastream with a presentation time of at least the T_(SAP) can be correctlydecoded using the information contained in the first multiplexedrepresentation starting at the I_(SAP) and no information before theI_(SAP).
 24. The system of claim 23, further comprising a multimediaadaptor configured to play back the first segment or subsegment of thefirst multiplexed representation of the streaming content.
 25. Thesystem of claim 23, wherein the processor is configured to request theselected first segment or subsegment of the first multiplexedrepresentation of the streaming content by using HTTP requests with URLsderived based on the information regarding component access points. 26.The system of claim 23, wherein the processor is further configured toswitch from the first multiplexed representation of the streamingcontent to a second multiplexed representation of the streaming contentby selecting a second segment or subsegment of the second multiplexedrepresentation of the streaming content based on received informationregarding CAPs and requesting the selected second segment or subsegmentof the second multiplexed representation of the streaming content fromthe network.
 27. The system of claim 26, wherein the first multiplexedrepresentation comprises a first version of a first media component anda first version of a second media component; and the second multiplexedrepresentation comprises the first version of the first media componentand a second version of the second media component.
 28. The system ofclaim 27, wherein: the first version of the first media componentcomprises an audio component; the first version of the media secondcomponent comprises a video component at a first video resolution or afirst bitrate; and the second version of the second component comprisesthe video component at a second video resolution or a second bitrate.29. A non-transitory computer readable medium with an executable programstored thereon, wherein the program instructs a microprocessor toperform the following steps: receive, from a network, informationregarding component access points (CAPS) of a first multiplexedrepresentation of a streaming content, wherein the first multiplexedrepresentation of the streaming content comprises a plurality of mediacomponents, wherein each group of CAPs of a plurality of groups of theCAPs is associated with a respective one of the plurality of the mediacomponents and each CAP defines an independently coded access unit forthe respective one of the plurality of media components and identifies aposition in the first multiplexed representation enabling playback forthe respective media component using the information contained in datain the first multiplexed representation after the respective CAP andindependently of information in the multiplexed representation beforethe respective CAP; identify a stream access point (SAP) in the firstmultiplexed representation of the streaming content based on theinformation regarding the CAPs, wherein the SAP identifies a position inthe first multiplexed representation enabling playback of a media streamusing the information contained in the first multiplexed representationstarting from that position onwards, wherein the SAP corresponds to aI_(SAP) and a T_(SAP), wherein at least one of the CAPs of each group ofthe CAPs identifies a position in the first multiplexed representationthat is different from the position in the first multiplexedrepresentation identified by the SAP, wherein at least one of the CAPsof each group of CAPS identifies a position in the first multiplexedrepresentation that is different from positions in the first multiplexedrepresentation identified by each of the CAPs in at least one of theother ones of the plurality of groups of the CAPs, and wherein: theI_(SAP) is a byte position in the first multiplexed representation, andthe T_(SAP) is an earliest presentation time, for any access unit of themedia stream, that all access units of the media stream with apresentation time of at least the T_(SAP) can be correctly decoded usingthe information contained in the first multiplexed representationstarting at the I_(SAP) and no information before the I_(SAP); select afirst segment or subsegment of the first multiplexed representation ofthe streaming content based on the SAP; and request the selected firstsegment or subsegment of the first multiplexed representation of thestreaming content from the network.
 30. The non-transitory computerreadable medium of claim 29, wherein the program further instructs themicroprocessor to receive the requested first segment or subsegment fromthe network and play the received first segment or subsegment.
 31. Thenon-transitory computer readable medium of claim 29, wherein the programfurther instructs the microprocessor to change multiplexedrepresentations from the first multiplexed representation of thestreaming content to a second multiplexed representation of thestreaming content by: selecting a second segment or subsegment of asecond multiplexed representation of the streaming content based on theinformation regarding CAPs, and requesting the selected second segmentor subsegment of the second multiplexed representation of the streamingcontent.
 32. The non-transitory computer readable medium of claim 31,wherein: the first multiplexed representation of the streaming contentcomprises a first version of a first media component and a first versionof a media second component; and the second multiplexed representationof the streaming content comprises the first version of the first mediacomponent and a second version of the second media component.
 33. Thenon-transitory computer readable medium of claim 32, wherein: the firstversion of the first media component comprises an audio component; thefirst version of the second media component comprises a video componentat a first video resolution or a first bitrate; and the second versionof the second media component comprises the video component at a secondvideo resolution or a second bitrate.
 34. The non-transitory computerreadable medium of claim 31, wherein the program further instructs themicroprocessor to: receive the requested first segment or subsegmentfrom the network; play back the requested first segment or subsegment;receive the requested second segment or subsegment from the network; andplay back the requested second segment after playing back the requestedfirst segment or subsegment.
 35. The method of claim 1, wherein the SAPcomprises a Closed GoP random access point in which all the accessunits, in decoding order, starting from the I_(SAP) can be correctlydecoded, wherein decoding results in a continuous time sequence ofcorrectly decoded access units with no gaps.
 36. The method of claim 35,wherein the SAP is configured to be used for randomly accessing a mediapresentation at a start-up of the media presentation or after a seekingoperation or error event.
 37. The method of claim 35, wherein the SAP isconfigured to be used for switching between two representations wherebyfor seamless switching a switch-from representation is presented up tothe T_(SAP) and each media stream in a switch-to representation ispresented from the SAP starting from the T_(SAP).
 38. The method ofclaim 35, wherein the information regarding the CAPs includes an @startwithSAP attribute that, when present and having a value greaterthan 0, specifies that each media segment in associated representationsstarts with a stream access point type that is less than or equal to thevalue of this attribute value in each media stream.
 39. The method ofclaim 14, wherein the SAP comprises a Closed GoP random access point inwhich all the access units, in decoding order, starting from theI_(SAP)can be correctly decoded, wherein decoding results in acontinuous time sequence of correctly decoded access units with no gaps.40. The system of claim 23, wherein the SAP comprises an Open GoP randomaccess point in which there are some access units in decoding orderfollowing I_(SAU) that cannot be correctly decoded and have presentationtimes less than the T_(SAP), wherein I_(SAU) is a greatest position inthe first multiplexed representation such that all access units of themedia stream with a presentation time of at least T_(SAP) can becorrectly decoded using data in the first multiplexed representationstarting at I_(SAU) and no data before I_(SAU).
 41. The method of claim1, wherein the SAP comprises a Closed GoP random access point in which afirst access unit in decoding order in the media stream starting fromI_(SAU) is not a first access unit in presentation order, whereinI_(SAU) is a greatest position in the first multiplexed representationsuch that all access units of the media stream with a presentation timeof at least T_(SAP) can be correctly decoded using data in the firstmultiplexed representation starting at I_(SAU) and no data beforeI_(SAU).